Table 1.

Circulating levels of sex hormones in female subjects during the study trials

	Estrogen, pg/mL	Progesterone, ng/mL	FSH, mIU/mL	LH, mIU/mL
Control	133 ± 73	0.1 ± 0.1	4.7 ± 2.5	5.3 ± 5.9
Fentanyl	107 ± 53	0.8 ± 1.2	3.0 ± 3.0	5.2 ± 6.6

Values are means ± SD. Data were assessed from arterial blood samples; n = 5. Control, trial with intact leg muscle afferent feedback; fentanyl, trial with attenuated leg muscle afferent feedback using fentanyl blockade; FSH, follicle-stimulating hormone; LH, luteinizing hormone. No differences between the trials, P ≥ 0.31.